The case reads 0% but will charge the buds when plugged in.

My case reads zero through the app and the indicator light stays red whenever I plug it in. It still charges the buds when plugged in or on a wireless charging pad. I opened the case and the contacts all appear clean and the battery doesn't appear swollen. I can feel the case warm slightly when it's plugged in leading me to believe the battery isn't discharging properly, but I can't seem to find a replacement battery anywhere, including the official Samsung parts site. Does anyone know where I might be able to get the battery and the circuit for said battery?